1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a method for controlling an image forming apparatus having a density sensor for measuring developer density of an image formed on an image carrier during the driving of the image forming apparatus.
2. Description of the Related Art
An image forming apparatus is an electric device for printing images on a recording medium. Generally, a copier, a printer, a multifunctional device, and a facsimile are included in the image forming apparatus. The image forming apparatus is classified into an inkjet type image forming apparatus and an electro-photographic process image forming apparatus based on the method used for recording an image on the recording medium. The electro-photographic process image forming apparatus records an image on the recording medium by using a developing unit, and then firmly fixes the recorded image on the recording medium by pressing the recording medium with the recorded image at a high temperature.
FIG. 1 is a diagram illustrating a conventional developing unit of a laser beam printer which is capable of printing multi-color images.
Referring to FIG. 1, the conventional developing unit 10 includes an image carrier 11, an optical beam scanning means 13 for forming a latent image by irradiating an optical beam on the image carrier 11, at least one or more developer carriers 12 for applying the developer based on the latent image formed on the image carrier 11, and transferring units 16 and 17 for transferring the image formed on the image carrier 11 onto the recording medium. The image carrier 11 can be implemented as a belt type or as a roller type as shown in FIG. 1. As an example, the transferring unit 17 is provided as an intermediate transfer belt (ITB) that is used in the developing unit of the image forming apparatus having a plurality of developer carriers 12 for printing images.
The developing unit 10 needs to control the amount of developer (Toner Area Coverage, or TAC) applied for forming images on a surface of the image carrier 11 in order to manage a quality of printing. Accordingly, the developing unit 10 includes a color toner density sensor (CTD sensor) 15 for measuring developer density of the image formed on the surface of the image carrier 11.
Generally, an optical sensor is used as the CTD sensor 15. The optical sensor outputs a varied level of signals according to the amount of reflected light from the image carrier 11. The optical sensor 15 includes a light source for irradiating a predetermined amount of light to the image carrier 11, and a light receiving unit for measuring an amount of light reflected from the image carrier 11.
For accurately measuring the developer density of the image carrier 11 during the driving of the image forming apparatus, a reference value for comparing a developer density of an object image during the driving of the image forming apparatus must be accurately setup.
However, the sensitivity of a conventional CTD sensor 15 may be easily varied according to changes in the printing environment, such as by the replacement of the image carrier and the aging of the image carrier. That is, the density sensor 15 is very sensitive to the changes in the printing environment. The above problems of the conventional CTD sensor 15 may cause inaccurate references to be setup for comparisons. Accordingly, the developer density of the image may not be accurately controlled, and allow the quality of printing images to degrade. Also, the image forming apparatus may be suddenly stopped by such an error in the CTD sensor 15. For overcoming the above problems, various conventional methods have been introduced for correcting the sensitivity of the CTD sensor 15 in response to changes in the printing environment. However, none of the introduced conventional methods can fully correct the sensitivity problems of the CTD sensor 15.
Accordingly, a need exists for a system and method for accurately correcting the sensitivity of the CTD sensor 15 in response to various driving environments of the image forming apparatus.